通過連接從超過2個mysql表中獲取數據。

Question

這是我的表格結構。

Table1 // it has 4 colums,that saves all the question posted by user 

id|question|answer|postby| 

Table2 //it has 2 colums, that saves all the signed up users 

id|username|email| 

Table3 //it saves that which question is read by which user. 

id|reader_id|question_id| 

注：reader_id是表2

問題的ID：我們需要找出那些沒有被特定用戶閱讀的問題。

Answer 1

select * from table1 where id not in (
    select question_id from table3 where reader_id = [particular user id] 
) 

Answer 2

FROM表1 SELECT問題其中id NOT IN（SELECT question_id FROM表3，其中reader_id IN（SELECT ID FROM表2其中username = 'XXXX'））

Answer 3

試試這個：

SELECT t1.* 
FROM table1 t1 
LEFT JOIN 
    (SELECT t3.* 
    FROM 
    table2 t2 
    JOIN table3 t3 ON t3.reader_id=t2.id 
    WHERE t3.reader_id=SOME USER)t ON t.question_id=t1.id 
WHERE t3.id IS NULL;